The present invention pertains generally to hard magnetic alloys and in particular to hard magnetic alloys comprising iron, boron, and lanthanides.
Iron alloys, including iron-boron alloys, have been used extensively as magnets, both soft and hard. A hard magnetic alloy is one with a high coercive force and remanence, whereas a soft magnetic alloy is one with a minimum coercive force and minimum area enclosed by the hysteresis curve.
Permanent magnets are generally made from hard magnetic materials because a large magnetic moment can exist in the absence of an applied magnetic field. Presently a wide variety of hard magnetic materials are known; however, all of them exhibit specific characteristics which render them suitable for some application but not for others.
The highest-performance permanent magnets are made from rare-earth, transition-metal, inter-metallic compounds such as SmCo.sub.5 or alloys closely related to it. Examples of these alloys are disclosed in U.S. Pat. No. 3,558,372. These alloys have magnetic properties which are extremely good for almost every application. The disadvantages are that they contain very expensive elements. They contain 34 percent rare earth by weight, and cobalt is a very expensive transition metal, currently in short supply. A second problem is that to get maximum performance, alloy processing of a rare earth permanent magnet is very complicated. Many of the techniques to get such performance are proprietary and not generally disseminated. A third problem is that high coercive forces are only available for a limited range of compositions, which means that the ability to change characteristics such as saturation magnetization are also limited.
Magnets which do not contain rare earths generally have much lower coercive forces than those of SmCo.sub.5 and related alloys. The various forms of ALNICO, for example, have coercive forces in the range of 600-1400 Oe, which is low for many applications. ALNICO alloys also contain a large amount of cobalt, which is expensive and in short supply. The advantage of ALNICO alloys is that they do have large values of saturation magnetization.
There are other permanent magnet materials often used. Various kinds of ferrites are available very cheaply, but generally they have both low coercive forces and low values of magnetization, so that their main virtue is very low cost. MnAlC alloys have no cobalt or other expensive elements and are beginning to be used. There again the coercive force and performance are lower than the SmCo.sub.5 class of alloys, although the cost is also lower. Cobalt-iron alloys including an addition of nickel, such as, U.S. Pat. Nos. 1,743,309 and 2,596,705 have hard magnetic properties, but generally do not have a large magnetic hysteresis.